Unable to turn on long DTMF tones. S6 on EE Network - 6.0.1

[AC Question]

Since the most recent update my DTMF tones have switched to short and the option to change it has disappeared, my house alarm dialer will only work with the long tones, leaving me unable to acknowledge if it is activated.

This is a massive problem, because the dialer will just keep calling me until I respond with the keypad reply it requires!